Generally, this kind of front detrailleur is so constructed that a chain guide having inner and outer plates is supported to reciprocate through operation of a pair of linkage members connected to a fixing member fixed to a seat tube at the bicycle frame. A return spring having a coiled portion and first and second retaining ends and biasing the chain guide in the direction of backward movement is interposed between the chain guide and either the fixing member or one linkage member. A control wire attached to one linkage member is pulled to move the chain guide forwardly against the return spring, the wire being released to move the chain guide backwardly by a restoring force of the return spring.
Since the front derailleur is mounted onto the seat tube between the front and rear wheels, mud splashed from the rear wheel lodges in the gaps between the coiled wires of the return spring, resulting in a reduction in the spring action of the return spring, creaks at the coiled portion, and a tendency to rust.
Conventionally, a cylindrical member with a bore having a diameter slightly larger than an outer diameter of the coiled portion of the return spring is fitted on the return spring to thereby prevent attachment of the mud.
The cylindrical member in the conventional front derailleur is bottomed and provided at the bottom with a center bore and at the peripheral wall with a guide slot extending axially and receiving the first end of the return spring. Further, such conventional cylindrical member is fitted onto the coiled return spring so that a pivot pin is inserted into the coiled spring and into the center bore at the cylindrical member. The pivot pin connects the one linkage member and chain guide to thereby assemble the cylindrical member with the return spring. Hence, a problem has been created in that the spring and cylindrical member are not stationary to each other, thus making assembly thereof difficult.